No evidence for transgenerational immune priming in <i>Daphnia dentifera</i>

Transgenerational immune priming increases the resistance or tolerance of offspring from pathogen-exposed parents. This phenomenon can have substantial ecological and evolutionary consequences, highlighting the importance of understanding its generality both across host taxa and within a host species. Transgenerational immune priming has been reported in multiple invertebrate species, but the robustness and generality of priming in offspring is not clear. For instance, prior studies using Daphnia spp., which are freshwater invertebrates and dominant grazers, found contrasting results for transgenerational immune priming. Some studies found transgenerational immune priming for certain genotypes and in specific contexts while others found no evidence of transgenerational immune priming. Our study addresses multiple questions about transgenerational immune priming using three clones of Daphnia dentifera and three pathogen species varying in their fitness impacts on hosts. We collected offspring from mothers either unexposed or exposed to pathogens and then exposed offspring to either the same pathogen as the maternal exposure (a homologous challenge) or a different pathogen (a heterologous challenge). We measured offspring susceptibility for all treatments and pathogen burden for the two 'obligate killer' pathogens. We did not find any evidence of transgenerational immune priming related to offspring susceptibility. Following a heterologous challenge, one clone showed a reduction in spore burden of one pathogen, which could be an indication of increased tolerance, but no significant reduction in susceptibility. Our results, paired with mixed support from previous studies, suggest that transgenerational immune priming is not a consistent or strong factor influencing disease dynamics in the D. dentifera system.